Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 37 Rb 85 84.9117897379(54) 0.7217(2) 85.4678(3) g 87 86.9091805310(60) 0.2783(2) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page